How does "Scope" tab in "Client Scope" work? What does it affect?

Hi.

I’m exploring KC’s functions, and “Client Scopes” is still uncharted land. If you create client scope “myscope” with mapper “Full user name” for example and assign this client scope to a client and later try to get a token from this client with scope “myscope” - you’ll get full username in your access token.
But what does tab “Scope” of Client Scope form affect? You can select any realm role or any client role in this tab, what is a correct usecase for using this function?

Thanks